Influence of the S:Ni ratio in raw materials on the NixSy electrocatalysts

Nickel sulfides have been considered to be among the most effective oxygen evolution reaction (OER) electro-catalysts. Until now, there are many different nickel sulfides, such as Ni3S2, NiS, Ni3S4, NiS2, etc. In this paper, we set out to explore the influence of the S:Ni ratio in raw materials on the different nickel sulfides. With the characterizations of XRD, XPS, SEM, TEM and BET, the relevance between the molar ratio of S:Ni in raw materials and stoichiometric ratio, microscopic structure and OER performance are discussed. According to the results of the experiments, the Ni3S4 derived from the 3:1 M ratio of S:Ni in raw material exhibits the smallest overpotential (245 and 314 mV to achieve 10 and 20 mA/cm(2)) and Tafel slope (81.5 mV/dec). Meanwhile, theoretical calculation of Delta G(H2O*) indicate that the adsorption energy in Ni3S4 is much closer to the IrO2 than other nickel sulfides, which are in good agreement with the OER performance of electrochemical measurements.